1. Field of Invention
The present invention relates generally to converter circuits, and in particular to converter circuits used to drive gas discharge lamps.
2. Background Art
Current gas discharge lamps generally require a high power factor and good (i.e., less than 20%) total harmonic distortion (THD). These requirements coupled with output current crest factors imposed by manufacturers of gas discharge lamps, drive designers to utilize various conditioning circuits in the front end of current ballast designs. One of the primary design requirements is of course cost, and any use of conditioning circuits on the front end adds to the cost of the ballast design.
A ballast which accomplishes good THD and power factor, while also maintaining a crest factor within the requirements of bulb manufacturers' recommendations (1.7) without the need for a front end correction circuit is very desirable for cost and efficiency reasons but has been elusive due to the conflicting requirements listed above.
Additionally, active correction circuits are switching power systems on their own. The resulting efficiency of the total lighting product is the product of the efficiencies of the two converters, the active front end converter and the ballast power transfer converter efficiency. This limits the total system efficiency to the high eighties even when the ballast converter efficiency is very high.